Although the number of case reports and epidemiologic evidence of orogenital transmission of HIV infection has increased in recent years, little is known about biological, behavioral or social risk factors that may be associated with this mode of transmission. We propose to identify risk factors for oral acquisition of HIV infection using a case-control study design. By using a uniform method of identifying recent seroconverters (dual or "detuned" enzyme immunoassay) who report only receptive oral sex as a mode of transmission, a uniform oral and periodontal exam, sexually transmitted disease screening, and standardized questionnaires, to measure biological, behavioral and sociodemographic data, we will study a question of great concern to communities at risk of HIV infection. The Specific Aims of this proposal are: 1. To assess whether host oral environment including signs and symptoms of periodontal disease (e.g. gingival bleeding or loss of attachment), and/or oral health practices are associated with increased odds of oral acquisition of HIV infection. 2. To assess which specific orogenital sexual practices and oral exposure to ejaculatory fluids (such as swallowing or not swallowing semen) are associated with increased or decreased odds of oral acquisition of HIV. 3. To assess whether comorbid conditions documented within the seroconversion period (e.g. sexually transmitted disease such as gonorrhea, chlamydia and other viral infections such as HSV-1 or 2) are associated with increased or decreased odds of oral acquisition of HIV. 4. To assess whether non-injecting substance use which may modify the oral or naso-pharyngeal mucosa and/or sexual behavior is associated with increased or decreased odds of oral acquisition of HIV. The case-control design cannot estimate infectivity or the rate of oral HIV infection, but is the only feasible way to study factors which may influence the risk of oral infection. Identification of the cofactors for orogenital HIV acquisition will provide us with the kind of data that can be used by AIDS prevention programs and by members of AIDS risk groups themselves so that the risk for HIV transmission can be lowered even further. For this reason, this study addresses a crucial public health goal, one that is long overdue for careful epidemiological study.